1. Fields of the Invention
The present invention relates generally to systems and methods for detecting ice or fluid on a surface, such as on a roadway or aircraft wing or tail, and more particularly, to the use of a remote optical sensor that is located at or near the area or aerodynamic surface where icing most likely occurs. The sensor is coupled by a light channel to a logic unit and ice indicator positioned along a roadway or in a control center or cockpit, which indicator can warn and differentiate type, rate, and thickness of substance accumulation and ice accretion.
2. Discussion of the Prior Art
Aircraft technology has progressed by leaps and bounds over the past 60 years of powered flight. However, a nagging problem since the inception of IFR flight has been the unresolved safety concern surrounding in-flight icing. Thousands of deadly accidents have been attributed to airframe icing. This unfulfilled need has been most emphatically driven home by a recent commercial accident which has taken the lives of many passengers.
Modern aircraft are equipped with a wide variety of equipment which detect and warn pilots of hazardous weather conditions. Notwithstanding these advances, modern aircraft are still not adequately equipped to detect and warn pilots of ice adhering to critical parts of their airframe. Federal Regulations prohibit flight in icing conditions that exceed those defined in F.A.R. Part 25, Appendix C. Nonetheless, flights are regularly made by commercial aircraft on authorized flights into freezing drizzle or freezing rain, where the size of supercooled water droplets, suspended in air and ready to freeze on the first solid object they touch, exist in the atmosphere and pose the greatest icing hazard. Freezing drizzle, in particular, is a silent invisible killer which is only made worse by darkness and its accumulation on aircraft parts not visible to the pilot under any circumstances, such as, tail surfaces where ice build-up is especially lethal.
A fundamental problem according to the Airline Pilots' Association, is that there exists a serious disharmony between the criteria used for certification of an aircraft and the criteria used for dispatch and operation of that aircraft. Thus, there is a long felt need for a reliable method of detecting critical icing conditions from the cockpit so that once icing conditions are encountered, they may be rapidly and accurately detected and the pilot can then either remove the ice with anti-ice systems or alter course and get out of the hazardous condition before a dangerous amount of ice accumulates on critical aerodynamic surfaces.
Over the years a wide variety of aircraft ice detection systems have been invented employing virtually every known physics principle, with limited success. Just to name a few, such systems have included, for example, a pneumatic system of Blaha in U.S. Pat. No. 5,301,905; the temperature systems of Kleven in U.S. Pat. No. 4,980,673 and Hansman in U.S. Pat. No. 5,313,202; the vibrational systems of Marxer in U.S. Pat. No. 4,553,137 and Koosmann in U.S. Pat. No. 4,611,492 (Assignee Rosemount); the force system of Daniels in U.S. Pat. No. 4,775,118 (Assignee Boeing); the ultrasonic system of Watkins in U.S. Pat. No. 4,604,612; and the flush mounted electrical/temperature hybrid system of Weinstein (Assignee NASA) in U.S. Pat. No. 4,766,369. None of these systems has achieved any widespread commercial success.
It is also known to use aircraft ice detection systems having optical components. For example, in a system to Mischoud in U.S. Pat. No. 5,014,042 there is disclosed a system which employs an optical channel employing a prism sensor at one end of an optical channel comprising a fiber optic bundle which totally reflects light internally in a no ice condition, but refracts some of the incident light externally of the system in the presence of water or ice thereby detectably reducing or eliminating the amount of internally reflected light. In that system, rain produces a low frequency modulation of the quantity of reflected light which is demodulated to differentiate rain from ice. Mischoud does not disclose or suggest the use of an optical sensor having a single optical fiber, or a sensor that can distinguish between the type of ice using optical scattering and reflection, or further, that can differentiate between types of ice and de-icing fluid.
It is also been known to use an infrared laser light source in a remote location in the wing leading edge for deriving signals representative of icing used to provide a cockpit alarm as in the system to Federow U.S. Pat. No. 5,296,853. However, such system does not suggest the use of a laser as a light source remote from the optical sensor in the wing and coupled thereto by a light channel.
There are several ice detection systems in very limited use on present large aircraft. One such system uses a fuselage mounted 1" diameter gear that continually rotates when the aircraft is in flight. If any ice builds up on the gear, the ice will brush up against a microswitch as the gear rotates and will trigger a caution light to the flight crew. The system works so poorly that flight crews generally ignore the warnings, deferring to an also ineffective visual inspection. The main drawbacks of the system are the moving parts, the microswitch itself freezing up, and the fact that the system is not mounted on the wings or tail--the location where ice build-up is critical.
Another such known system is an ultrasonic ice detector currently being tested on small passenger jets--aircraft particularly susceptible to ice. The sensor uses about 4" of wing space and consists of a disk that vibrates continuously. Any ice build-up changes the frequency of the vibration and thus alerts the pilots. There are also several drawbacks with this unit, too. First, it is also a non-solid state product. The cold high altitude temperatures and temperature changes make frequency calibration unreliable. Secondly, due to the size of the unit and the flat wing space required it cannot be mounted on the curved leading edge of the wing-the very first area to be affected by ice build-up. By the time any ice would cover this unit, the accumulation could be severe. The other drawbacks of this system are high cost, environmentally exposed wing-mounted electronics, and a lack of redundancy-only one sensor per aircraft.
See also, U.S. Pat. Nos. 4,803,470; 5,270,537; 5,484,121; 5,528,224 and 5,596,320 for additional ice detection systems and methods. At the present time there are no known, reliable and cost-effective electronic ice detection systems for small or mid-size aircraft, and that also can be used to detect ice on other surfaces, such as on roadways or carburetor induction systems.
Accordingly, as indicated above, there is still a long felt need for an effective ice detection system for all aircraft, large or small, and it is the primary object of this invention to fill this need with a small, non-intrusive, solid state, low cost, remote ice detection system, which can be redundantly located at the critical surfaces most likely to be affected by ice build-up. The need further exists for ice detection systems and methods that can easily and cost effectively be employed to detect ice on other types of surfaces, such as roadways and carburetor induction systems.